Conventionally, saturated esters such as n-propyl acetate, isobutyl acetate and n-butyl acetate have been commonly used as solvents and reaction solvents and are industrially important compounds. These saturated esters are generally produced by an esterification reaction resulting from condensation of a corresponding alcohol and carboxylic acid.
However, in such esterification reactions, the reaction equilibrium cannot be shifted to the product (saturated esters) side unless water as a by-product is removed from the system, and it is industrially difficult to obtain a high raw material conversion rate and reaction rate. Since the latent heat of vaporization of water is much higher than that of other organic compounds, there is also the difficulty of consuming a large amount of energy during the separation of water by distillation.
On the other hand, unsaturated esters, which contain an unsaturated group such as an allyl group, a methacrylic group or a vinyl group, in the alcohol portion of an ester, can be produced industrially through an oxidative carboxylation reaction or the like between a corresponding olefin and a carboxylic acid.
In particular, it is well known that unsaturated group-containing esters can be produced by reacting a corresponding olefin, oxygen and a carboxylic acid in the gas phase in the presence of a palladium catalyst, and there are numerous known documents regarding this production. For example, PTL 1 describes how allyl acetate can be produced industrially with an extremely high yield and high space-time yield by reacting propylene, oxygen and acetic acid in the presence of a palladium catalyst in the gas phase.
In addition, there are numerous known documents describing a reaction of adding hydrogen to a carbon-carbon double bond of an unsaturated group-containing ester such as allyl acetate, that is, a hydrogenation reaction (also referred to as “hydrogen addition”).
For example, PTL 2 discloses a method of producing n-propyl acetate by hydrogenating allyl acetate using a nickel catalyst as a catalyst for the hydrogenation reaction, in other words, a hydrogenation catalyst. PTL 3 describes a method of producing n-propyl acetate by using a silica-supported palladium catalyst, an alumina-supported palladium catalyst, a sponge nickel or the like. According to the PTL 3, an allyl acetate conversion rate of substantially 100% can be achieved, while an n-propyl acetate selectivity of 99.0% or more is also achieved. Here, PTL 3 describes that in the case of synthesizing allyl acetate by passing a raw material gas containing propylene, oxygen and acetic acid in the presence of a palladium catalyst in the gas phase, the reactor outlet gas thus obtained is cooled and separated into a non-condensed component and a condensed component, and the crude allyl acetate liquid obtained as the condensed component is distilled to obtain an allyl acetate-containing liquid containing allyl acetate from the top of the column. When this allyl acetate-containing liquid is used as a raw material liquid and is hydrogenated, the target product, n-propyl acetate, can be obtained.
On the other hand, it is also known that when allyl acetate is synthesized by reacting propylene, oxygen and acetic acid in the presence of a palladium catalyst in the gas phase, by-products are produced, and for example, PTL 4 describes acrolein and diacetates (allylidene diacetate: CH2═CH_CH(—OCOCH3)2, 1,3-diacetoxypropene, and the like) as the by-products included in the condensed component.